So you've just built a totally sweet new social app and you can't wait for people to start using it, but there's a problem: when people join they don't have any friends on your site. They're lonely, and the experience isn't good because they can't use the app with people they know. You could ask them to search for and add all their friends, but you know that every other app is asking them to do the same thing and they're getting sick of it. Or they tried address book import, but that didn't totally work, because they don't even have all their friends' email addresses (especially if they only know them from another social networking site!). What's a developer to do?
One option is the new Social Graph API, which makes information about the public connections between people on the Web easily available and useful. You can make it easy for users to bring their existing social connections into a new website and as a result, users will spend less time rebuilding their social networks and more time giving your app the love it deserves.
Here's how it works: we crawl the Web to find publicly declared relationships between people's accounts, just like Google crawls the Web for links between pages. But instead of returning links to HTML documents, the API returns JSON data structures representing the social relationships we discovered from all the XFN and FOAF. When a user signs up for your app, you can use the API to remind them who they've said they're friends with on other sites and ask them if they want to be friends on your new site.
